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Nestling characteristics and identification of the lesser spotted eagle Aquila pomarina, greater spotted eagle A. clanga, and their hybrids

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Abstract

The lesser spotted eagle Aquila pomarina and the greater spotted eagle A. clanga are closely related endangered raptors whose taxonomic status, field identification, and ultimately conservation, have been complicated due to morphological similarity. However, the partial overlap in morphological features may also involve hybrids, which are known to exist, but which have so far been poorly described. This study investigated spotted eagle nestlings in Estonia, pre-identifying them according to mitochondrial DNA, nape patch and the appearance of their parents. Relative size of bill and toes (corrected for nestling growth) enabled us to separate the smaller A. pomarina, but hybrids were as large as A. clanga. All three groups had distinct plumages with hybrids being intermediate; the separation was clearest using both size and plumage indices. In all, 164 of 168 birds were correctly identified using a three-step procedure, separating: (1) A. clanga, having no nape patch; (2) 9 of 13 hybrids according to plumage index; and (3) the remaining hybrids by their large size (at least two features over the mean+2 SD values of A. pomarina). Knowing the sex helped to interpret size, but not plumage, characteristics, and its overall value for assisting identification was not high. The results support the view that spotted eagles with intermediate characters are usually hybrids which can be recognised by their appearance.

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Acknowledgements

We thank all those people who participated in searching for nests, describing nestlings and blood sampling; we are particularly indebted to Raivo Endrekson, Tarmo Evestus, Kristo Lauk, Riho Männik, Pauli Saag, Gunnar Sein, Urmas Sellis, Indrek Tammekänd, Aarne Tuule and Eet Tuule for their contribution. The inventories of nests were partly funded by the Estonian Centre of Environmental Investments in the frame of the implementation of the national management plan for the greater spotted eagle. Laboratory work was performed at the Institute of Molecular and Cellular Biology (Department of Evolutionary Biology, University of Tartu). We are also grateful to Dick Forsman, Jüri Kärner, Vilju Lilleleht, Rimgaudas Treinys and an anonymous referee for their comments on the manuscript. The work complies with the current laws in Estonia.

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Authors and Affiliations

  1. Institute of Zoology and Hydrobiology, University of Tartu, Vanemuise 46, 51014 , Tartu, Estonia

    Ülo Väli & Asko Lõhmus

Authors
  1. Ülo Väli
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  2. Asko Lõhmus
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Correspondence to Ülo Väli.

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Communicated by F. Bairlein

Appendix

Appendix

Table 6 lists the characteristics of the 13 hybrid nestlings from eight nest sites.

Table 6 Characteristics of the 13 hybrid nestlings from eight nest sites (A–H; the young from different years numbered). Measurements are in mm except in last three columns where index scores are shown. See Methods and Tables 1, 2 for detailed description of the characteristics
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Väli, Ü., Lõhmus, A. Nestling characteristics and identification of the lesser spotted eagle Aquila pomarina, greater spotted eagle A. clanga, and their hybrids. J Ornithol 145, 256–263 (2004). https://doi.org/10.1007/s10336-004-0028-7

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